442 PROCEEDINGS OP THE ACADEMY OP 



This beautiful little shell is very closely allied to C. sericea of Conrad, (Jour. 

 Acad. Nat. Sci., Pbila., New Series, vol. 4, page 281, pi. 46,) but differs in 

 being uniformly more broadly ovate in form, and in having less elevated and 

 less distinctly incurved beaks, while its concentric markings are not near so 

 strongly defined. 



Locality and Position. Same as last. We also have a fragment of appa- 

 rently the same species from the Yellow Stone River, in upper part Fort Pierre 

 Group. 



Genus CARDIUM, Linnajus. 

 Cardium (Hejiicardiom?) curtcm. 



Shell trigonal, gibbous, closed ; anterior side more or less rounded ; posterior 

 side distinctly truncated and transversely flattened; base forming an elliptic 

 curve; postero-basal extremity angular; hinge very short; beaks elevated, 

 pointed, distinctly incurved, and a little oblique at the immediate points; pos- 

 terior umbonal slopes prominent and angular from the beaks to the base. Sur- 

 face ornamented by about forty five regular, distinct radiating costae, usually 

 a little wider than the deep grooves between, and always simple on the gibbous 

 portion of the valves, but apparently sometimes bifurcating on the truncated 

 posterior side. (Hinge teeth unknown.) 



Height, 1-74 inch; breadth, 1-80 inch ; convexity, l-30inch. 



This is a peculiar shell, not liable to be confounded with any other species 

 with which we are acquainted. It seems to form a connecting link between 

 the singular group Hemicardium and the true typical Cardiurnms ; being one of 

 the many instances met with in the study of fossil species of a form connect- 

 ing groups which in our existing fauna appear to be separated by rather 

 marked differences. 



Locality and position. Head Gros Ventres River, where it occurs with a 

 large Inoceramus in a gray sandstone, probably of Cretaceous age. Fragments 

 of apparently the same Cardium were brought by Capt. Simpson's Expedition 

 from a yellow sandstone near Bear River, Utah. 



Cardium pertenue. 



Shell rather small and very thin, broad ovate in form, its height being greater 

 than its length, very ventricose ; anterior and basal margins regularly rounded ; 

 posterior side subtruncate ; hinge margin short; beaks elevated, gibbous, dis- 

 tinctly incurved, and very nearly central; posterior umbonal slopes promi- 

 nently rounded. Surface ornamented by fine lines of growth and a few con- 

 centric wrinkles near the free border ; on the posterior half of the valves 

 there are also some fifteen to twenty nearly obsolete radiating costa;, which 

 impart to the posterior and postero-basal margins a distinctly crenulated 

 outline. 



Height, 0*64 inch ; diameter, from the anterior to the posterior margin, 0-59 

 inch ; convexity, 0-50 inch. 



This species is of the same type as Cardium sulquadratum and C. rarum of 

 Evans and Shumard, (Trans. Acad. Sci., St. Louis, vol. 1, p. 39); from both 

 of which it may be at once distinguished by its much more elevated beaks 

 and greater height in proportion to its length. These three species belong to 

 a small group having close relations to Protocardium, being concentrically 

 striated or nearly smooth on the anterior half of the shell, with faint indica- 

 tions of radiating costae behind. These markings, however, are not so distinct 

 and regular as on the. typical species of Protocardium ; the concentric striaa 

 being merely very fine, obscure lines of growth, and the plications often almost 

 entirely obsolete. 



Locality and position. Deer Creek, near the North Branch of Platte River, 

 from the upper part of the Fort Pierre Group, or the lower part of the Fox 

 Hills Beds. 



[Dec. 



